The hydroformylation or oxo process is known as a method for the production of saturated aldehydes from olefins, carbon monoxide, and hydrogen in the presence of a catalyst, in which the method involves addition of one hydrogen atom and one formyl group (—CHO) onto a C═C bond. Generally, these aldehydes are subjected to condensation, followed by hydrogenation to give the corresponding alcohols with the longer chain.
The hydroformylation can be exemplified by the preparation of octanol (2-ethylhexanol) from propylene using a rhodium catalyst.
Octanol is mainly used as a raw material for obtaining plasticizers for PVC, such as DOP, and used as an intermediate in the preparation of synthetic lubricants, surfactants or the like. Propylene is injected together with a synthesis gas (H2+CO) into an oxo reactor using a catalyst to generate n-butylaldehyde and iso-butylaldehyde. The produced aldehyde mixture and catalyst mixture are sent to a separation system, and are separated into hydrocarbons and catalyst mixture. Then, the catalyst mixture is recycled to the reactor, and the hydrocarbons are sent to a stripper. The hydrocarbons in the stripper are stripped with the fresh synthesis gas, and the unreacted propylene and synthesis gas are recovered to the oxo reactor. Butylaldehydes are sent to a fractionation column, and separated into n-butylaldehyde and iso-butylaldehyde, respectively. The n-butylaldehyde is introduced from the bottom of the fractionation column into an aldol condensation reactor, followed by condensation and dehydration to give 2-ethylhexenal. The 2-ethylhexenal is sent to a hydrogenation reactor, and thus octanol (2-ethylhexanol) is produced by hydrogenation. The reactants in the outlet of the hydrogenation reactor are sent to a fractionation column, followed by separation of light/heavy ends to give octanol products.
The hydroformylation may be performed in a continuous, semi-continuous, or batch types, and a typical hydroformylation reaction system is a gas or liquid recycle system. On the other hand, in the hydroformylation, it is important to increase reaction efficiency by improvement in contact between liquid and gaseous starting materials, which has been conventionally accomplished by using a continuous stirred tank reactor (CSTR). In addition, in U.S. Pat. No. 5,763,678 , disclosed is a hydroformylation process in a series of loop-type reactors which functions as a continuous stirred tank reactor. However, there are limitations in the improvement of the hydroformylation efficiency by the above methods, and it is hard to obtain desirable aldehyde products using a single reactor. Thus, desirable aldehyde products can be generally produced by a longer reaction retention time or two or more reactors connected in series.